Columns used in liquid chromatography typically comprise a tubular body enclosing a packed bed of porous chromatography medium through which a carrier liquid flows, with separation taking place by material collection between the carrier liquid and solid phase of the porous medium. Typically, the medium is enclosed in the column as a packed bed formed by consolidating a suspension of discrete particles, known as slurry that is pumped, poured, or sucked into the column. Consolidation of the slurry into a consolidated packed bed is achieved by compressing the slurry so that it is packed into a volume, which is less than the volume that it would have occupied if it had been allowed to settle under the influence of gravity to form a sedimented bed. The efficiency of subsequent chromatographic separation relies strongly on 1) the liquid distribution and collection system at the fluid inlet and outlet of the packed bed, 2) on the spatial orientation (also know as the packing geometry) of the media particles in the packed bed, and 3) on the compression of the packed bed. If the compression of the packed bed is too low then chromatographic separations performed on that bed suffer from “tailing” and, generally, such insufficiently compressed beds are unstable. If the compression of the packed bed is too high then chromatographic separations performed by the bed suffer from “leading” and such over-compressed beds can affect throughput and binding capacity, and, in general, give much higher operating pressures. If the compression is optimum, then the separation peaks formed during use exhibit much less leading or tailing and are substantially symmetrical. The optimum degree of compression required for a column is determined experimentally for each column size (width or diameter), bed height, and media type.
Prior to any separation process the column and the bed have to be prepared. Before the column is filled with slurry the column, hoses to/from the column and valves connected to the column often needs to be primed. This means to purge away air from the column and from the hoses connected to the system. Usually liquid is flowed through the system and column to purge the air away. After the column has been filled, either by means of the liquid flow through the bed support or through spray nozzles, it can be pressurized to force the last remaining air out of the column. This can be achieved by continuing to pump liquid into the column against a closed outlet and then opening the outlet to release pressure or by running the moveable adapter downwards fast, thereby expelling air through the bed supports, possibly one at a time. After the priming the column often also needs to be sanitized. Then the column can be filled with slurry and the packing procedure takes place. The process of bed formation is called ‘the packing procedure’ and a correctly packed bed is a critical factor influencing the performance of a packed bed. One of the primary goals of the packing procedure is to provide a bed, which is compressed by the optimum amount of compression, i.e. the optimum compression factor. The height of the bed which often is user defined when it is optimally compressed is called the target compressed bed height.
Large-scale columns, can be prepared by suctioning or injecting into the column a predetermined volume of slurry having a specified or known concentration of media particles. Once the predetermined volume of slurry has been delivered into the column it needs to be consolidated and compressed by for example moving a movable adapter down the longitudinal axis of the column towards the bottom of the column, normally at a constant speed push both liquid and particles towards the bottom of the column. The excess liquid during this procedure is expelled at the column outlet, while the media particles are retained by means of a filter material, a so-called ‘bed support’, with pores too small to allow the media particles to pass through. The packing process is complete once the packed bed has been compressed by the optimum degree of compression. The packing process is considered successful if the compressed bed allows for a good and robust chromatographic performance. There are alternative ways of packing that can be used in this invention. For example a flow can be applied to force the particles in the slurry to move towards the outlet of the column, instead of moving an adapter downwards. A further alternative is to use spray nozzles spraying in slurry until a packed bed is achieved. These methods will be further described below. However, packing such an optimally compressed bed of chromatography media in a chromatography column by manual means is not easy to accomplish in practice due to the fact that the quality of the final packed bed depends to a great extent on the skill of the operator. During filling and subsequent packing of the column, the operator manually selects and adjusts all packing parameters such as valve positions, pump speed, adapter's speed of movement, etc. The operator has to measure the slurry concentration in order to decide how much slurry that should be filled into the column. If the measure of the slurry concentration is not exact (which is often the case because it is hard to measure the slurry concentration exactly) the volume of the slurry filled into the column is not optimal and the consolidated bed will settle at a bed height that was not expected (as calculated from the measured slurry concentration) and hereby the target compression can not be achieved at target bed height. Furthermore, the operator also has to judge the point when the adapter starts compressing the bed. This point is used to calculate how much further the adapter must move in order to obtain the required amount of compression. Mistakes in the selection of any of the packing parameters normally lead to a poorly performing column. Further, in columns equipped with a transparent tube it may be difficult, and in columns equipped with a non-transparent tube such as stainless steel it is impossible, to judge by eye when compression of the bed actually starts and a significant error at this point makes it impossible to obtain an optimally compressed bed.
There is also a risk of damaging the media and the column if the user takes wrong decisions.
When the media bed has been packed in the column an efficiency test is sometimes performed in order to judge if the packed bed is good enough for use. This could be for example a pulse test, a transitional test or a test of pressure/flow properties. If the results from the tests show that the packed bed is of unacceptable quality the bed needs to be unpacked and then repacked in order to provide a packed bed that is acceptable.
All these steps that need to be performed are of course time consuming. Operator errors are common which leads to time consuming and costly repacking.
Therefore, there is a need for a system and method for the accurate and reproducible packing of chromatography media into chromatography columns.